Your supplier signed a self-billing agreement with you three years ago. You have issued invoices on their behalf ever since without incident. You send the first one through KSeF and the gateway rejects it:
Kontekst 6343060594 nie jest uprawniony do wystawienia faktury
w imieniu sprzedawcy (NIP: 1234567890)
Translation: the authenticated context is not authorised to issue invoices on behalf of that seller. The contract is still valid. What is missing is the second layer, a technical permission the seller has to grant you separately inside KSeF. The Ministry of Finance states this directly: the buyer may issue an invoice on the seller's behalf, but the seller must first grant that permission in the system (KSeF 2.0 Q&A).
Here is what to set up, how the invoice looks inside the FA(3) schema, when exactly the seller has to approve it, and who bears the consequences when something goes wrong.
Three conditions, all mandatory
Self-billing sits in Article 106d of the Polish VAT Act, and that provision did not change when KSeF became mandatory. What changed is the technical layer around it.
1. A contract between seller and buyer. The law does not prescribe a form, but written form is the only defensible choice. The contract should identify the parties, the scope of transactions covered, the validity period and, above all, the invoice approval procedure.
2. An approval procedure spelled out in that contract. It can be active (the seller confirms each invoice) or passive, sometimes called silent (no objection within an agreed window counts as approval). Both are permitted. The timing is what matters, and that is covered below.
3. A permission granted inside KSeF. The seller signs into KSeF, enters the buyer's NIP (Polish tax identification number) and grants a dedicated self-billing permission. This can be done in the free Taxpayer Application provided by the Ministry of Finance or in commercial software integrated through the API. Permissions granted in KSeF 1.0 do not carry over to KSeF 2.0, so companies that ran self-billing before February 2026 had to re-grant them in the Certificates and Permissions Module.
One system limitation is worth knowing. KSeF does not allow you to narrow the self-billing permission, for example to original invoices only, excluding corrections. Any scope limit has to come from the contract, not from system settings. A buyer holding the permission can also delegate it further to their own staff.
How the invoice looks in the FA(3) schema
The most common beginner error is swapping the parties. On a self-billed invoice the layout is identical to an ordinary one.
FA(3) element Content Podmiot1 (Party 1) Seller, the supplier of goods or services Podmiot2 (Party 2) Buyer, who physically issues the document P_17 Value "1" marks self-billing Visualisation note The word "samofakturowanie" (self-billing) Podmiot3 (optional) Role 10, invoice issuer
The buyer does not become the seller. They issue a document in someone else's name and on their behalf, and the system recognises them by permission, not by position on the invoice. In Biurko the is_self_invoicing flag on an invoice maps directly to the P_17 annotation in the generated XML, so it cannot be dropped by oversight at send time.
Note that the self-billing permission does not cover VAT RR invoices, the documents issued to flat-rate farmers. Those have a separate permission in KSeF and a separate FA_RR schema, and the farmer must additionally file a declaration in the system naming the buyer.
Approval timing: where companies lose the deduction
This is the newest and most expensive change in practice. In February 2026 the Director of the National Revenue Information Service issued an individual tax ruling (ref. 0112-KDIL1-3.4012.874.2025.2.KK) holding that confirmation of a buyer-issued invoice should happen immediately before the document enters legal circulation, meaning before the XML file is sent to KSeF.
The ruling goes further. In the authority's view the approval must cover the XML file itself, not a PDF draft, even where the PDF matches the structured invoice that follows. The consequence: a buyer who approves invoices only after sending them to KSeF may lose the right to deduct input VAT.
Two caveats. First, an individual ruling binds only the case it was issued for and is not legislation. Polish tax advisers broadly agree that this requirement does not follow directly from the VAT Act. Second, it nonetheless signals how the authorities will act, and rebuilding the process around it is safer than betting on a friendlier line later.
In operational terms this means one thing: the buyer must be able to generate the invoice XML, share it with the seller for approval, and only then transmit it. Silent approval still works, but the objection window now runs before transmission rather than after. For companies processing hundreds of documents a month, that is a genuine workflow redesign.
Who is liable for what
Three layers of liability get conflated in most conversations. Keep them apart.
Party Responsibility Seller (Podmiot1) Settling output VAT on the sale. Self-billing does not shift the tax obligation. The invoice remains their document Buyer (Podmiot2) Accuracy of the issued document and adherence to the approval procedure. Risks losing deduction under Article 88(3a)(5) of the VAT Act Both Contractual consequences: penalties, claims, cost of corrections. Governed by the contract, not the statute
Article 88(3a)(5) is the pivotal provision here: invoices issued by the buyer that were not approved by the seller do not support a reduction of output tax. The whole liability structure therefore rests on whether you can prove approval and when it happened.
The practical conclusion: keep an approval log. For the active model, email correspondence with the XML attached is enough. For the silent model you need evidence of when the file reached the seller and when the objection window closed. Without that, you have nothing to defend with.
A separate issue is a mistake in buyer data. KSeF does not verify counterparty details and will accept an invoice with the wrong NIP. Corrective notes were abolished, so the only route is a correction to zero against the wrong NIP plus a fresh original invoice with the correct one. In self-billing, the correction is issued by the same entity that issued the original, under the same permission.
When self-billing in KSeF simply will not work
Not every self-billing arrangement can run inside the system.
The permission cannot be granted to an entity that does not use a Polish NIP. If your supplier relationship involves a foreign company without one, the invoice is produced outside KSeF under the previous rules. The Ministry of Finance confirms that invoices issued by foreign entities under self-billing with a Polish seller are not covered by mandatory KSeF.
The exception concerns intra-Community supplies of goods. A buyer from another EU member state using a VAT UE number assigned for intra-Community transactions may issue an invoice in KSeF on behalf of a Polish seller once the permission is granted. May, not must.
Checklist before your first self-billed invoice
Confirm the agreement contains a described approval procedure, not just consent to issue invoices.
Set the approval point before transmission to KSeF and define the objection window.
Ask the seller to grant the self-billing permission in KSeF against your NIP. The contract does not substitute for it.
Verify that permissions granted before February 2026 were re-issued in the Certificates and Permissions Module.
Build a process for sharing the XML with the seller before sending, and archive proof of approval.
Make sure your system sets P_17 to "1" and prints the self-billing annotation on the visualisation.
Agree separately who issues corrections and within what deadline. KSeF will not enforce that split for you.
Summary
Self-billing in KSeF is no harder than before, but it is more formal. The contract and the system permission are two independent layers, and the moment of approval has stopped being an organisational detail and become a condition of VAT deduction.
Biurko supports the self-billing annotation in the FA(3) structure, translates KSeF rejection messages into plain language (including the missing-permission error shown above), and lets you run multiple companies from one panel with operation-level permissions. That last part matters when you sit on both sides of the transaction.
Create a free Biurko account and walk through the invoice flow before you issue your first self-billed document.
FAQ
Is a self-billing agreement enough to issue an invoice in KSeF? No. Beyond the contract, the seller must grant the buyer a self-billing permission directly in KSeF. Without it the system rejects the file, even if the agreement has been in force for years.
Who pays the VAT on a self-billed invoice? The seller. Self-billing transfers the act of issuing the document to the buyer, not the tax obligation. The invoice remains the seller's document and they settle output VAT on it.
When does the seller have to approve the invoice? According to the Director of the National Revenue Information Service, approval should occur before the XML file is sent to KSeF and should cover the content of that file. Approving after transmission may cost the buyer the input VAT deduction.
Can a foreign company issue invoices on my behalf in KSeF? Only if it uses a Polish NIP or, for intra-Community supplies of goods, an EU VAT number. In other cases the invoice is produced outside KSeF under the previous rules.
Who issues a correction to a self-billed invoice? The same entity that issued the original, under the same permission. KSeF cannot restrict the permission to original invoices only, so any division of duties has to come from the contract.